Generally, an electronic power steering system (EPS) is an apparatus for ensuring steering stability of a vehicle and provides a torque in the direction that a driver steers using a motor for smooth handling.
Unlike the existing hydraulic power steering (HPS), the EPS may improve steering performance and steering feel by controlling an operation of a motor according to driving condition.
A torque load about a steering axis, a steering angle, and an angular velocity of steering need to be measured for the EPS to provide an appropriate torque.
A conventional steering structure includes an input axis coupled with a steering wheel, an output axis joined with a pinion which is coupled to a rack bar at a wheel and a torsion bar which connects the input axis and the output axis.
When a steering wheel is rotated, rotation power is delivered to the output axis and directions of wheels are changed by the operation of a pinion and a rack bar. Here, when a resistance force is great, the input axis becomes more rotated so that the torsion bar becomes twisted, and a magnetic field type torque sensor measures the degree of twist of the torsion bar.
The torque sensor is provided to be accommodated in an upper casing and a lower casing with a rotor, a stator, a collector and a circuit board, and the torque sensor provided as such is accommodated in a housing to connect with the input axis and the output axis. Here, a stator holder is fixed in the axis direction by coupling the upper casing and the lower casing.
However, there is a problem in that the stator holder vibrates in a case in the case of not being fixed in a direction perpendicular to the axis direction, i.e. the horizontal direction. When the stator holder vibrates as such, a gap of the stator tooth delivering a magnetic force is changed, and thus there is a problem in that reliability of the torque sensor operation is lowered.